Light sources, of the lyman type, emitting a spectrum in the ultra-violet range



LIGHT soUR'cEs', OF THE LYMAN TYPE, EMITTIN A SPECTRUM IN THE ULTRA-VIOLET RANGE Filed NOV. 16, 1964 29', 1967 M R P. MORLAIS ETAL G 3,339,109

United States Patent 3,339,109 LIGHT SOURCES, OF THE LYMAN TYPE, EMIT- TING A SPECTRUM IN THE ULTRA-VIOLET RANGE Maurice Ren Pierre Morlais and Stphane Jean-Pierre Alfred Robin, Rennes, France, assignors to Centre National de la Recherche Scientifique, Paris, France, a state administration Filed Nov. 16, 1964, Ser. No. 411,304 Claims priority, application France, Nov. 25, 1963, 954,913 9 Claims. (Cl. 315238) It is known that, in the remote ultra-violet range, the obtainment of stable and windowless sources involves great difiiculties. Of course there are known light sources produced by the condensed discharge of capacitors in capillary tubes, these sources being called Lyman sources and emitting a continuous spectrum in the remote ultraviolet range. However, up to this time, these sources required the presence of a gas in the capillary tube to start the discharge. The necessity of the presence of the gas is further indicated by recent publications, such for instance, as the following ones:

W. R. Hunter, Proceedings of the Xth' Colloqium Spectroscopicum Internationale, Washington, 1962,

F. J. Comes and H. G. Salzer, Z. Naturf., 18 (1963), page 594.

Now the presence of a gas in the capillary tube has many drawbacks:

It makes it difiicult to obtain a high vacuum in the measurement apparatus, in particular when use is made of windowless sources;

The gas absorbs some radiations;

It complicates the mounting of the source due to the fact that it requires means for the feeding said gas;

It increases the cost of operation of the source by the price of the gas that is used, which is generally a rare gas of high purity, therefore expensive.

Now we have found that it is possible to obtain an ultra-violet source by the condensed discharge of capacitors in capillary tubes in the absence of a gas by providing in the source a high vacuum (pressure lower for instance than 1()- and even 1O mm. of mercury) by making use, to start the discharge, of auxiliary electrodes bringing into play a sliding spark.

We will recall the principle of the known sliding spark starting system. It is known that, if between two electrodes located in a vacuum and at a distance from each other of 23 mm. there is applied a potential difference of some thousand volts, no current passes. On the contrary, if there is interposed between these two electrodes an insulating material (the term insulating being considered from the electrical point of view), an electric current flows on the surface of this material, producing a socalled sliding spark.

The invention is concerned with a light source emitting a spectrum in the remote ultra-violet range and even in the extreme ultra-violet range, said source comprising two electrodes, a first one and a second one connected together by a capillary tube, the shape of the second electrode being such that it permits observation of the light emitted along the axis of the capillary tube, and at least one first capacitor. The invention is characterized by the fact that, in the capillary tube, there is provided a very high vacuum and that the system further comprises a third electrode and a fourth electrode separated from each other by a layer of dielectric so as to form a sliding spark starting device located in the vicinity of one of the two first mentioned electrodes, at least a second capacitor, means for charging said first capacitor and said second capacitor under a voltage of several thousands of volts, and means -for producing, at predetermined times,

the discharge of said second capacitor along the dielectric substance comprised between said third electrode and said fourth electrode.

Such a source permits of obtaining, according to the conditions of operation (nature of the capillary tube, capacity, self inductance and loading voltage of the capaci tor, etc.) either a continuous spectrum of high intensity, in particular a continuous spectrum in the remote ultraviolet range, this being particularly useful for the study of the absorption spectrum in the remote ultra-violet range, or a spectrum of intensive emission lines in the extreme ultra-violet range (from to 1000 A.) on a relatively little intensive continuous background.

A preferred embodiment of the present invention will be hereinafter described with reference to the appended drawings, given merely by way of example, and in which:

FIG. 1 is a diagrammatic part sectional view of a light source made according to the present invention;

FIG. 2 is a simplified diagram of this source with its electric feed circuits.

The source of FIGS. 1 and 2 comprises a fluidtight vessel or container 1 limiting a space 20 wherein can be obtained, by means of a vacuum source 2, a vacuum of the order of 10"*, or even 10- mm. of mercury. Vessel 1 constitutes the grounded negative electrode, the positive electrode or anode 3 being connected to electrode 1 through a capillary tube 4 in which there is a vacuum. Fluidtight connection between capillary tube 4 and anode 3 is ensured by means of toroidal shape packings 9 and 10, whereas fiuidtightness on the side of container 1 is obtained by means of packings 11 and 22. The system of electrodes has a coaxial arrangement, vessel 1 being prolonged by a metallic casing 12 which constitutes the external part (grounded) of the coaxial system.

The sliding spark starting device comprises two electrodes 5 and 6 separated from each other by a dielectric layer 7.

Anode 3 is connected, at 8, to the armature of a set of capacitors C Electrode 5 may be connected at 18, to the armature of a set of capacitors C electrode 6 being grounded.

Capillary tube 4 is made of a dielectric material, advantageously alumina or silica. But it might also be made of other dielectric materials such as tefion. The dielectric of the spark starting device may be made, for instance, of silica, alumina, mica, permitting of easily ensuring the passage of the starting spark through the vacuum.

The observation spectrograph is diagrammatically shown at 13, with its input opening located at 14, in the wall of vessel 1.

Advantageously, supplementary means are provided for reducing the noxious eifects of the vaporization produced by the discharges, in particular of the vaporization of capillary tube 4, said means comprising, for instance, a protecting cap 15, for instance of tantalum, on the side of anode 3 and/or protection rings 16, in particular of aluminum on the side of opening 14.

By way of example, the width L of body 12 may be 100 mm. the length D of capillary tube 4 being 100 mm. and the inner diameter e of said capillary tube 4 ranging from 4 to 8 mm.

This light source is fed, for instance, as illustrated by FIG. 2. A high voltage source 21 (for instance of 30 kv.) is inserted between the ground and one end of a resistor 19 the other end of whichis connected to a terminal b, whereas electrode 3 and armature 8 are connected to a terminal a. Armature 18 is connected to a terminal c and electrode 5 is connected to a terminal a. A rotary switch successively produces the following connections:

Connection of terminals a and 12 together, to charge capacitors C from source 21 through resistor 19;

Connection of terminals b and c together for charging capacitor C from source 21 through resistor 19;

Connection of terminals and a' together to produce a sliding spark between electrodes and 6 with a discharge of capacitor unit C this spark then producing the main discharge between the main electrodes 3 and 1 through capillary tube 4, which discharges capacitor-s C A new cycle may then be repeated.

In a modification (not shown), terminals a and b are permanently connected together. Terminal c is permanently connected with another voltage source of a value ranging for instance from 4 to kv. Finally a controlled connecting device (comprising for instance a thyratron, the grid of which receives, at a predetermined rate, starting pulses from a pulse generator) ensures the discharge of C through the sliding spark.

Concerning C we have used two capacitors of 0.11 microfarad, whereas for C we have used, in two series of experiments successively, on the one hand two Safco- Trevoux DR 861 capacitors, each of two microfarads, and on the other hand one or several Bosch capacitors of 0.5 microfarad and of very low self inductance (20 millimicrohenrys).

It has been found that, due to the fact of the extremely low self inductance of Bosh capacitors, we obtained, with such capacitors, much shorter, and therefore much more powerful discharges and a more continuous spectrum than with the Safco-Trevoux capacitor, although the energy consumed in a flash is greater with the Safco- Trevoux than with the Bosch capacitors.

In all cases we may obtain discharges which have, in the remote ultra-violet range and even in the extreme ultra-violet range, a continuous spectrum, on which are superposed some emission lines.

On the other hand, by modifying the characteristics of the main electric circuit, and in particular by reducing the capacity of capacitors C (about 0.1 microfarad) and the voltage of source 21 (from 10,000 to 15,000 volts), it is possible to obtain a spectrum rich in intensive lines in the whole ultra-violet range (in particular from 100 to 2000 A.). As the power of every discharge is reduced, it is possible to operate the source at a sutficient frequency (for instance from to 100 discharges per second) to permit the recording of spectrums by means of a photoelectric receiver connected with a pen recorder of ordinary type. Reproductibility of the successive discharges is sufficient to ensure a good stability. The presence of a great number of intensive lines with a small continuous background in the spectrum is advantageous with a dispersive apparatus with a tangential defraction grating with which it would be difficult to separate the diiferent interference orders with a continuous spectrum.

On the other hand, it has been found that with a source according to the present invention, the amount of material that is evaporated is small, which has a great advantage, in particular in that it avoids the soiling of the slot and of the network of the dispersive apparatus.

Finally, it will be noted, that it is possible to utilize higher charging voltages and therefore higher discharge powers by filling with an insulating oil of high dielectric strength the cavity 17 located between piece 12 and capillary tube 4.

In a general manner, while we have in the above description disclosed what we deem to be a practical and efficient embodiment of our invention, it should be well understood that we do not wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of our invention as comprehended within the scope of the appended claims.

What we claim is:

1. A source of light in the ultra-violet range which comprises, in combination,

a container forming a fluidtight closed chamber,

a first electrode forming a portion of the inner wall of said chamber,

a second electrode rigid with said container,

a capillary tube forming a communication between said two electrodes,

a source of vacuum in communication with said chamber for producing therein and in said capillary tube a vacuum of at least 10 mm. of mercury,

a third electrode in said chamber,

a fourth electrode in said chamber,

a layer of dielectric material in said chamber interposed between said third electrode and said fourth electrode and in contact therewith to form a sliding spark device, said dielectric material layer being located in said chamber sufficiently close to one of said two first mentioned electrodes to start a spark between said two first mentioned electrodes when a sliding spark is produced between said third and fourth electrodes,

a first capacitor having its conducting surfaces connected with said first and second electrodes, respectively,

a second capacitor,

means for charging said first capacitor and said second capacitor under a voltage of several thousands of volts, and

means for connecting the conducting surfaces of said second capacitor with said third and fourth electrodes respectively, so that said second capacitor discharges along said layer of dielectric material, between said third and fourth electrodes, whereby a spark is then produced between said first and second electrodes.

2. A source according to claim 1 wherein the two first mentioned electrodes and the capillary tube are disposed coaxially with one another.

3. A source according to claim 1 wherein said capillary tube is made of a dielectric material.

4. A source according to claim 1 wherein said capillary tube is made of alumina.

5. A source according to claim 1 wherein said capillary tube is made of silica.

6. A source according to claim 1 further including a protecting cap carried by said second electrode opposite the end of said capillary tube nearest to said second electrode, so as to reduce the effects resulting from vaporization of said capillary tube.

7. A source according to claim 1 further including protecting rings carried by said container opposite the end of said capillary tube remotest from said second electrode, so as to reduce the effects resulting from vaporization of the capillary tube.

8. A source of light in the ultra-violet range which comprises, in combination,

a container forming a fluidtight closed chamber,

a first electrode forming a portion of the inner wall of said chamber,

a second electrode rigid with said container,

a straight capillary tube open at both ends and forming a communication between said two electrodes,

the wall of said chamber being provided with a hole in line with said capillary tube for placing said chamber in communication with an apparatus to be used with the source of light,

a source of vacuum in communication with said chamber for producing therein and in said capillary tube a vacuum of at least 10- mm. of mercury,

a third electrode in said chamber,

a fourth electrode in said chamber,

a layer of dielectric material in said chamber interposed between said third electrode and said fourth electrode and in contact therewith to form a sliding spark device, said dielectric material layer being located in said chamber sutficiently close to one of said two first mentioned electrodes to start a spark between said two first mentioned electrodes when a sliding capacitor and said third electrode, whereby a sliding spark is produced between said third and fourth spark is then produced between said third and fourth electrodes, electrodes, which initiates a spark between said first a voltage source of several thousands of volts having and second electrodes.

two terminals, a first one and a second one, 5 9. A source of light according to claim 8 which further a first capacitor having two conducting surfaces, a first comprises,

one connected to said source first terminal and to a protecting tantalum cap carried by said second elecsaid first electrode, and a second one connected to trode opposite the end of said capillary tube nearer said second electrode, to said second electrode, and a second capacitor having two conducting surfaces, at 10 protecting aluminum rings carried by the wall of said first one connected to said source first terminal and container around said hole thereof. to said fourth electrode, and a second one, and switch means for performing the following three cone en s C ed nections, successively: UNITED STATES PATENTS between said source second terminal and said second 15 conducting surface of said first capacitor, between said source. second terminal and said second I conducting surface of said second capacitor, and JOHN CKERT Prlmary Ex'ammer' between said second conducting surface of said second KRAFT, SANDLER, Assistant Examiner-Y- 2,937,299 5/1960 Nolan 315241 X 

1. A SOURCE OF LIGHT IN THE ULTRA-VIOLET RANGE WHICH COMPRISES, IN COMBINATION, A CONTAINER FORMING A FLUIDTIGHT CLOSED CHAMBER, A FIRST ELECTRODE FORMING A PORTION OF THE INNER WALL OF SAID CHAMBER, A SECOND ELECTRODE RIGID WITH SAID CONTAINER, A CAPILLARY TUBE FORMING A COMMUNICATION BETWEEN SAID TWO ELECTRODES, A SOURCE OF VACUUM IN COMMUNICATION WITH SAID CHAMBER FOR PRODUCING THEREIN AND IN SAID CAPILLARY TUBE A VACUUM OF AT LEAST 10-4 MM. OF MERCURY, A THIRD ELECTRODE IN SAID CHAMBER, A FOURTH ELECTRODE IN SAID CHAMBER, A LAYER OF DIELECTRIC MATERIAL IN SAID CHAMBER INTERPOSED BETWEEN SAID THEIR ELECTRODE AND SAID FOURTH ELECTRODE AND IN CONTACT THEREWITH TO FORM A SLIDING SPARK DEVICE, SAID DIELECTRIC MATERIAL LAYER BEING LOCATED IN SAID CHAMBER SUFFICIENTLY CLOSE TO ONE OF SAID TWO FIRST MENTIONED ELECTRODES TO START A SPARK BETWEEN SAID TWO FIRST MENTIONED ELECTRODES WHEN A SLIDING SPARK IS PRODUCED BETWEEN SAID THIRD AND FOURTH ELECTRODES, A FIRST CAPACITOR HAVING ITS CONDUCTING SURFACES CONNECTED WITH SAID FIRST AND SECOND ELECTRODES, RESPECTIVELY, A SECOND CAPACITOR, MEANS FOR CHARGING SAID FIRST CAPACITOR AND SAID SECOND CAPACITOR UNDER A VOLTAGE OF SEVERAL THOUSANDS OF VOLTS, AND MEANS FOR CONNECTING THE CONDUCTING SURFACES OF SAID SECOND CAPACITOR WITH SAID THIRD AND FOURTH ELECTRODES RESPECTIVELY, SO THAT SAID SECOND CAPACITOR DISCHARGES ALONG SAID LAYER OF DIELECTRIC MATERIAL, BETWEEN SAID THIRD AND FOURTH ELECTRODES, WHEREBY A SPARK IN THEN PRODUCED BETWEEN SAID FIRST AND SECOND ELECTRODES. 